Vascular regression precedes motor neuron loss in the FUS (1-359) ALS mouse model

Objective: Amyotrophic lateral sclerosis (ALS) presents a poorly understood pathogenesis. Evidence from patients and mutant SOD1 mouse models suggests vascular damage may precede or aggravate motor dysfunction in ALS. We have previously shown angiogenin (ANG) treatment enhances motor neuron survival, delays motor dysfunction and prevents vascular regression in the SOD1G93A ALS model. However, the existence of vascular defects at different stages of disease progression remains to be established in other ALS models. Here we assessed vascular integrity in vivo throughout different disease stages, and investigated whether ANG treatment reverses vascular regression and prolongs motor neuron survival in the FUS (1-359) mouse model of ALS. Methods: Lumbar spinal cord tissue was collected from FUS (1-359) and non-transgenic control mice at day 50, 90 and 120 of age. Vascular structures were determined by immunostaining against podocalyxin and α-smooth muscle actin in the spinal cord ventral horn and compared to motor neuron counts. Mice were intraperitoneally administered 1 µg of human ANG or vehicle triweekly from day 50 onward to assess effects on survival and vascular density. Gene expression and miRNA levels were analysed by qPCR and Taqman assay. Results: We found a significant decrease in vascular network density in lumbar spinal cords from FUS (1-359) mice by day 90 (non-transgenic: 12.49±0.25 mm blood vessels/mm2 n=7 vs transgenic: 11.40±0.37 mm/mm2 n=8, t-test: p<0.04), at which point motor neuron numbers were unaffected. Surprisingly, ANG treatment did not affect survival or counter vascular regression. Endogenous mAng1 and Vegf expression were unchanged at PND 50 and 90, however we found a significant decrease in miRNA 126 at PND 50 indicating vascular integrity in FUS mice may be compromised via an alternative pathway. Conclusion: Our study demonstrates vascular regression occurs prior to motor neuron degeneration in FUS (1-359) mice, and highlights that heterogeneity in responses to novel ALS therapeutics can already be detected in preclinical mouse models of ALS.